Virosome-formulated Plasmodium falciparum AMA-1 & CSP derived peptides as malaria vaccine: randomized phase 1b trial in semi-immune adults & children

Abstract

Background: This trial was conducted to evaluate the safety and immunogenicity of two virosome formulated malaria peptidomimetics derived from Plasmodium falciparum AMA-1 and CSP in malaria semi-immune adults and children.

Methods: The design was a prospective randomized, double-blind, controlled, age-deescalating study with two immunizations. 10 adults and 40 children (aged 5-9 years) living in a malaria endemic area were immunized with PEV3B or virosomal influenza vaccine Inflexal®V on day 0 and 90.

Results: No serious or severe adverse events (AEs) related to the vaccines were observed. The only local solicited AE reported was pain at injection site, which affected more children in the Inflexal®V group compared to the PEV3B group (p = 0.014). In the PEV3B group, IgG ELISA endpoint titers specific for the AMA-1 and CSP peptide antigens were significantly higher for most time points compared to the Inflexal®V control group. Across all time points after first immunization the average ratio of endpoint titers to baseline values in PEV3B subjects ranged from 4 to 15 in adults and from 4 to 66 in children. As an exploratory outcome, we found that the incidence rate of clinical malaria episodes in children vaccinees was half the rate of the control children between study days 30 and 365 (0.0035 episodes per day at risk for PEV3B vs. 0.0069 for Inflexal®V; RR = 0.50 [95%-CI: 0.29-0.88], p = 0.02).

Conclusion: These findings provide a strong basis for the further development of multivalent virosomal malaria peptide vaccines.

Trial registration: ClinicalTrials.gov NCT00513669.

Keywords: Tanzania; efficacy; immunogenicity; malaria; peptide; safety; vaccine; virosomes.

Conflict of interest statement

Competing Interests: NW, SAS and RZ were employees of Pevion Biotech Ltd. during the trial. RZ and GP are named as inventors in patents covering the vaccines tested. By the end of 2007, Mymetics S.A., Lausanne, Switzerland took over the responsibility of this project from Pevion Biotech Ltd. PC's curent affiliation is with F. Hoffmann-La Roche Ltd., Basel, Switzerland and RZ's current affiliation is with Lonza Ltd., Visp, Switzerland. This does not alter the authors' adherence to all the PLoS ONE policies on sharing data and materials.

Figures

Figure 1. Study flow chart.

Figure 2. Development of anti-AMA49-C1 and anti-UK-39 IgG ELISA endpoint titres in adults and children immunized with PEV3B or Inflexal®V.

Bars indicate 95% confidence intervals of the geometric mean (no bars are shown for adult Inflexal®V, n = 2). Participants were immunized on days 0 and 90 (see arrows).

Figure 3. Box-plots of the logarithms of the index of response (ratios of anti-AMA49-C1 and anti-UK-39 IgG ELISA endpoint to baseline titers) for samples taken at day 30, 90, 120, 180, and 365.

AP: adults PEV3B, AI: adults Inflexal®V, CP: children PEV3B, CI: children Inflexal®V. At all time points the logarithm of the index of response of AP and CP groups were significantly >0 (index of response >1, p<0.05). This was never observed for the AI and CI groups. Symbols indicate the level of significance for differences in the index of response between PEV3B and Inflexal®V groups within adults and children subjects (exact Wilcoxon test, *: p<0.05, **: p<0.01, ***: p<0.001).

Figure 4. Attack rates of first or only clinical malaria episodes in vaccinated children.

Kaplan-Meyer failure functions are shown for the intervals from 30 days after first vaccination (day 30) until the end of the study (day 365), from 30 days after first vaccination until second vaccination (day 90), and from 30 days after second vaccination (day 120) until study end (day 365). P-values for differences in failure functions between treatment groups are given (log-rank test). Note: the failure function in the third panel is not identical with the corresponding part of the failure function in the first panel, because of the occurrence of multiple events in the same individual during the course of the study.

Figure 5. Comparison of the integrated antibody responses against AMA49-C1 and UK-39 with the detection of malaria parasitaemia in PEV3B children during time periods Day 0–30, Day 0–120 and Day 0–365.

ΔAUC was calculated as the area under the log (antibody titer)-curve above the baseline antibody titer. ΔAUC values were compared between those PEV3B children who did not have positive smears for P. falciparum and those PEV3B children who were tested positive for parasites using Wilcoxon's test. The numbers (in brackets) in the bars indicate the number of PEV3B in each of the groups compared.